Lime plaster bubbling

[keithevans595]

Hello All,
Over two years ago I had the lower part of a chimney breast replastered with lime plaster. It was left to dry out for six months and then given a couple of coats of Earthborn paint.
After six to nine months the plaster started bubbling up, the worst can be seen in the photos which is about 3 inches across.
Recently other patches have started to appear.
For a bit of history and documented in an older discussion,
The house is Victorian, 140 years old.
The wall in quesion is a party wall and there is no cavity, the other side of the wall is my neigbhours living room.
My neighbour claims to have no damp problem?
There is plenty of airflow under the suspended floor and the base is concrete over a DPM plastic sheet over earth.

Any ideas greatfully received!

 

[Cubist]

To my admittedly unpracticed eye that looks like salt damage. You say this was a chimney breast. Salts from fires can build up in the masonry of the chimney stack and migrate through old AND new plaster to do this kind of damage. Sadly, I think there are few remedies that I've seen recommended that do not require the plaster to be stripped off and the underlying masonry treated.

Hopefully, another member will have some better advice.

 

[keithevans595]

Thank you Cubist, oddly it's not on the chimney breast, which has been fine. It's on the recess either side of the chimney and on a single skin wall!

 

[housegolem]

Luckily cubist has taken the fall for me ! and said what i was thinking.

My other thought was it looks quite pink and possibly gypsum, despite your posting its lime

As it so damaged it would be worth a scrape to see what/if anything is underlying

 

[keithevans595]

Thank you Housegolem, I can confirm it was lime plaster, I purchased it and mixed it for the plasterer!

 

[keithevans595]

I think I will scrape some of it off and see what appears below.
Will post further pictures later.

 

[Cubist]

Errr, if salts were only associated with fires. Sadly these elements are fairly common and can pop up in the oddest places.

 

[Stevers]

Is it stone or brick?
Another possibility is some sort of foreign inclusion under those patches causing the efflorescence. I saw something similar to this on my basement chimney breast and it seemed to be related to some rusty old steel fixings. Definitely wort a dig out to investigate and then try patching it again.

 

[keithevans595]

It's brick.
I'm going to dig out the worst patch and see what may be below.